The Obama administration is downplaying differences with Afghan President Hamid Karzai, calling him "a reliable partner." In a series of joint appearances on American television, Secretary of State Hillary Clinton and Defense Secretary Robert Gates talked about Afghanistan, Iran, and the upcoming nuclear summit in Washington.

Both Clinton and Gates say they understand the pressures on Hamid Karzai as a leader of a nation that has been a battleground for decades.

They say the Afghan leader is on track to visit Washington next month, despite his recent complaints about outside interference in his country.

Gates says President Karzai's controversial comments are the words of a man deeply concerned about his nation's sovereignty.

"I think he sees himself as the embodiment of Afghan sovereignty. And so he is sensitive to public statements that he thinks are not aimed not just at him, but at Afghanistan," Gates said.

In an interview aired Sunday on CBS's Face the Nation, Gates stressed the Karzai government is cooperating with U.S. military forces in Afghanistan.

Sitting side-by-side with the defense secretary, Clinton urged people not to over-react to Karzai's controversial statements - most notably his angry reaction to American news reports of official corruption in Afghanistan.

"We know how difficult it is sometimes for foreign leaders, not only in Afghanistan but elsewhere in the world to separate our free press and everything that it says and everything that it claims, from what our government policy is," Clinton said.

The joint interviews with three American television networks were broadcast on the eve of a nuclear summit in Washington that will be attended by more than 40 countries. Clinton told CBS the goal is to come together to keep nuclear arms out of the hands of terrorists and rogue states.

"We are seeking to get agreement and a work plan about how each country will do its best to better secure the nuclear material that it has within its borders to prevent the transit of nuclear material," Clinton said.

Gates and Clinton also talked about the threat posed by Iran's nuclear ambitions. On NBC's Meet the Press, Gates was asked if a nuclear-armed Iran is inevitable.

"We have not drawn that conclusion at all. And in fact, we are doing everything we can to try and keep Iran from developing nuclear weapons," Gates said.

Gates and Clinton were interviewed Friday at the Pentagon, one day after President Barack Obama signed a new nuclear arms reduction treaty with Russia.

Both extolled the virtues of the treaty, which must now be ratified by the U.S. Senate.

But a top Republican warned Sunday that a ratification vote will not come this year.

Tennessee Senator Lamar Alexander said there just is not enough time.

"With the Supreme Court pushing to the top of the agenda in the Senate and jobs, terror and debt being our major issues we should be worrying about, this is a treaty for next year," Alexander said.